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Increasing soil salinity is among the most detrimental threats restricting crop growth and productivity. In recent years, root inoculation with biofilm-forming plant growth-promoting rhizobacteria (PGPR) has been greatly interested in improving abiotic stress tolerance. This study examined the plant growth-promoting and biofilmforming potential of Azotobacter spp. obtained from maize rhizosphere, tested the salinity effect (up to 300 mM NaCl) on biofilm formation and exopolysaccharide (EPS) production, and evaluated their effect on maize growth at different concentrations (0, 50, and 150 mM) of NaCl under greenhouse conditions. The isolates produced different amounts of indole acetic acid (IAA) (from 0.96 to 7.51 µg mL −1 ) and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (from 2.10 to 19.50 µmol α-ketobutyrate mg −1 h −1 ). On average, the highest biofilm formation was found in A. chroococcum. Both biofilm formation and EPS production significantly increased (p < 0.05) at 150 and 300 mM NaCl in A. chroococcum SC8, A. beijerinckii SC10, and A. tropicalis SC4. These strains also significantly increased (p < 0.05) root depth by 44.1-55.9%, shoot height by 52.3-58.8%, fresh root weight by 42.8-52.4%, and fresh shoot weight by 44.6-53.6% at 150 mM NaCl compared with the uninoculated salinitystressed (control) treatment. Among plant growth regulators, higher biofilm formation and EPS production under increasing salinity exhibited better maize growth under salinity stress. Therefore, these respective strains might be promising bioinoculants for alleviating salinity stress in field experiments.

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Drought stress significantly reduces the growth and yield of cotton plants; therefore, reducing the damage caused by drought stress and improving the plant growth are highly important. The aims of this study were to investigate some of physiological and biochemical properties of cotton plants exposed to different drought levels and to determine the extent of improvement obtained by exogenous glycine betaine treatment for the damages caused by the adverse effects of drought. Three drought levels were created using PEG (Polyethylene glycol 6000) solution (0%, 10% and 20%). The drought groups were also divided into 2 subgroups by using 0 (control: glycine betaine solution was not applied) and 2 mM glycine betaine solution. The pot experiment was established in a growth chamber with 3 replications and the experiment repeated twice. The changes in the contents of contents of chlorophyll a and b, carotenoid, total dissolved protein, total dissolved carbohydrate and some nutrients were investigated. Chlorophyll a and b, calcium, magnesium, sodium and phosphorus concentrations were decreased, while carotenoid, total dissolved protein and carbohydrate, potassium contents increased with the increasing drought level. The results revealed that adverse effects of drought stress on cotton plants were alleviated by exogenous application of glycine betaine.

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